Influence of Fe-rich intermetallic inclusions on pit initiation on aluminum alloys in aerated NaCl
- Univ. of Illinois, Urbana, IL (United States)
The role that Al{sub 3}Fe intermetallic inclusions play during initiation of pitting corrosion on aluminum alloys was investigated in 0.6 M NaCl. In aerated solutions microscopic observations showed the growth of cavities in the host metal adjacent to inclusions. The rest potential of synthetic Al{sub 3}Fe was measured in aerated and deaerated NaCl solutions over a range of bulk pH values between 2 and 12 and was found to act as a cathode. In aerated solutions rotating disk electrode experiments on synthetic Al{sub 3}Fe electrodes verified that the cathodic reaction corresponded to the reduction of dissolved oxygen. With scanning pH microelectrodes, measurements were carried out near synthetic Al{sub 3}Fe electrodes which were coupled in a galvanic cell with Al-6061 in NaCl solution. In addition, the pH measured over Al-6061 at a distance of 25--30 {micro}m from the surface was observed to fluctuate between pH 4 and 8.5 for the first 2 h of immersion in NaCl solutions. Atomic force microscopy images of Al-6061 immersed in buffered aerated 0.6 M NaCl solution (pH 5.5) did not show any evidence of dissolution of the Al around intermetallics. These measurements support the view that Al{sub 3}Fe particles in Al-6061 serve as local cathodes, that a high pH develops around the intermetallic particles by dissolving alkaline cavities to evolve into a small number of rapidly dissolving acidic pits.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG02-91ER45439
- OSTI ID:
- 328209
- Journal Information:
- Journal of the Electrochemical Society, Vol. 146, Issue 2; Other Information: PBD: Feb 1999
- Country of Publication:
- United States
- Language:
- English
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